LU-11069 llite: correct file position after appending writes

In ll_file_io_generic() use the position returned in the kiocb to set
the returned file position. This ensures that the file position is set
correctly after an appending write. Add sanity test_23d() to check
that calling lseek() for the current offset returns the correct value
in this situation.

Lustre-change: https://review.whamcloud.com/32641



Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: Ic76ce49db6e87d5294e18546d5b75a12793aa99c
Reviewed-on: https://review.whamcloud.com/32661


Reviewed-by: Jinshan Xiong <jinshan.xiong@gmail.com>
Tested-by: Jenkins
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>